1. Field of the Invention
The present invention relates to a substrate for suspension for use in hard disk drives (HDDs), and so forth.
2. Background Art
In recent years, the spread of the Internet, etc. have generated demand for personal computers with increased information processing capacity and speed. To meet this demand, it has come to be necessary to increase the storage capacity and information transmission rate of HDDs incorporated in personal computers. As for a component called a magnetic head suspension, which is used to support a magnetic head in an HDD, a conventional suspension to which signal conductors made of gold wires or the like are connected has come to be replaced with a so-called wireless suspension of conductor-integrated type (flexor), in which signal conductors made of copper lines or the like are formed directly on a stainless-steel-made spring.
Demand on HDDs for use in a variety of small-sized devices including mobile phones has increased recently. HDDs therefore have been increased in the density of signal conductors, and, at the same time, magnetic heads have been decreased in size. Moreover, magnetic heads have come to have higher sensitivity, so that they are easily affected by static electricity with which they are charged. Therefore, one problem with small-sized magnetic head elements has been that, due to electric charges accumulated in sliders, they undergo change in their properties and are, in the worst case, destroyed.
There has been another problem in this field. High-frequency electrical signals have been more frequently used in recent years, in order to enhance the signal transmission rate and accuracy of HDDs. However, as the frequency of electrical signals to be transmitted increases, noises increase.
In order to solve the above problems, there has been used a means of grounding that connects electrically a slider and a suspension for a magnetic head via an electrically conductive resin placed between them. This means of grounding, however, has been disadvantageous in that since electrically conductive resins presently used for this purpose are not sufficient in conductivity, static electricity cannot be fully eliminated when an electrically conductive resin is used to connect a slider and a suspension. Moreover, the electrically conductive resins have been disadvantageous also in that since their adhesion is not satisfactory, they cannot bond a slider and a suspension with sufficiently high adhesion strength.
In order to overcome the above drawback, some proposals have been made in Patent Document 1. One of them is to connect electrically a grounding conductor connected to a slider and a metallic substrate by an electrically conductive resin. In this method, there is no need to use an adhesive whose adhesion is weak, such as an electrically conductive resin, to bond the slider and the metallic substrate, and an adhesive having strong adhesion can be used. This method, however, has been disadvantageous in that since an electrically conductive resin is used to connect the grounding conductor and the metallic substrate, the static electricity with which the slider is charged cannot be fully eliminated.
In order to prevent electrostatic destruction of a slider and to suppress the occurrence of noises, Patent Document 2 proposes a means of grounding in which a metallic pad is formed on the surface of an insulating layer layered over a metallic substrate, and a grounding terminal for connecting the metallic substrate and the metallic pad is formed in a through hole so made in the insulating layer and in the metallic pad that the metallic substrate is exposed. When such a means of grounding is used, it becomes possible to prevent electrostatic destruction of a slider by connecting a grounding conductor connected to the slider and the metallic pad, and, moreover, to bond the slider and the metallic substrate with sufficiently high strength. Furthermore, by placing the metallic pad in the vicinity of signal conductors formed on a substrate for suspension, it is possible to suppress the occurrence of noises on the substrate for suspension, and electrical signals transmitted by the signal conductors can thus be stabilized.
However, the means of grounding disclosed in Patent Document 2 has been disadvantageous in that since the metallic pad occupies a large area, it may be difficult to provide a substrate for suspension with this means of grounding. This is because there is a demand for substrates for suspensions that occupy only very small areas, since magnetic heads are getting smaller in size with the recent increase in the density of signal conductors in HDDs.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-164813
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2006-202359